spring之FactoryBean接口

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//该接口主要用于从spring中获取bean的时候如果实现了该接口会直接调用该接口中的getObject来获取bean
public interface FactoryBean {

	T getObject() throws Exception;

	
	Class getObjectType();

	
	boolean isSingleton();

}


/**
其在获取bean的时候判断是否实现了FactoryBean接口从这也可以看出如果一个类实现了FactoryBean接口但是我们想要返回他本身的实例,
我们可以在获取bean的时候在名字前面加&符号即可。
*/

protected Object getObjectForBeanInstance(
			Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {

		
		if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
			throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
		}

		//判断是否实现了FactoryBean接口或者以&开头
		if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
			return beanInstance;
		}

		Object object = null;
		if (mbd == null) {
			object = getCachedObjectForFactoryBean(beanName);
		}
		if (object == null) {
			// Return bean instance from factory.
			FactoryBean factory = (FactoryBean) beanInstance;
			// Caches object obtained from FactoryBean if it is a singleton.
			if (mbd == null && containsBeanDefinition(beanName)) {
				mbd = getMergedLocalBeanDefinition(beanName);
			}
			boolean synthetic = (mbd != null && mbd.isSynthetic());
			object = getObjectFromFactoryBean(factory, beanName, !synthetic);
		}
		return object;
	}

//这是从FactoryBean获取bean的代码
private Object doGetObjectFromFactoryBean(
			final FactoryBean factory, final String beanName, final boolean shouldPostProcess)
			throws BeanCreationException {

		Object object;
		try {
			if (System.getSecurityManager() != null) {
				AccessControlContext acc = getAccessControlContext();
				try {
					object = AccessController.doPrivileged(new PrivilegedExceptionAction